diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/AcmeJsonResource.java b/acme4j-client/src/main/java/org/shredzone/acme4j/AcmeJsonResource.java
index 255473af..75b8fc37 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/AcmeJsonResource.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/AcmeJsonResource.java
@@ -13,6 +13,7 @@
  */
 package org.shredzone.acme4j;
 
+import java.io.Serial;
 import java.net.URL;
 import java.time.Instant;
 import java.util.Objects;
@@ -32,6 +33,7 @@ import org.slf4j.LoggerFactory;
  * fetching it from the server if necessary.
  */
 public abstract class AcmeJsonResource extends AcmeResource {
+    @Serial
     private static final long serialVersionUID = -5060364275766082345L;
     private static final Logger LOG = LoggerFactory.getLogger(AcmeJsonResource.class);
 
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/AcmeResource.java b/acme4j-client/src/main/java/org/shredzone/acme4j/AcmeResource.java
index dfe52969..6f17114d 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/AcmeResource.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/AcmeResource.java
@@ -13,6 +13,7 @@
  */
 package org.shredzone.acme4j;
 
+import java.io.Serial;
 import java.io.Serializable;
 import java.net.URL;
 import java.util.Objects;
@@ -28,6 +29,7 @@ import edu.umd.cs.findbugs.annotations.Nullable;
  * using {@link #rebind(Login)}.
  */
 public abstract class AcmeResource implements Serializable {
+    @Serial
     private static final long serialVersionUID = -7930580802257379731L;
 
     private transient @Nullable Login login;
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java b/acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java
index 98497745..4f4d5e66 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java
@@ -15,6 +15,7 @@ package org.shredzone.acme4j;
 
 import static java.util.stream.Collectors.toUnmodifiableList;
 
+import java.io.Serial;
 import java.net.URL;
 import java.time.Duration;
 import java.time.Instant;
@@ -35,6 +36,7 @@ import org.slf4j.LoggerFactory;
  * Represents an authorization request at the ACME server.
  */
 public class Authorization extends AcmeJsonResource implements PollableResource {
+    @Serial
     private static final long serialVersionUID = -3116928998379417741L;
     private static final Logger LOG = LoggerFactory.getLogger(Authorization.class);
 
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java b/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
index 4a3ac1c1..53630f2f 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/Certificate.java
@@ -20,6 +20,7 @@ import static java.util.stream.Collectors.toUnmodifiableList;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.getRenewalUniqueIdentifier;
 
 import java.io.IOException;
+import java.io.Serial;
 import java.io.Writer;
 import java.net.MalformedURLException;
 import java.net.URL;
@@ -50,6 +51,7 @@ import org.slf4j.LoggerFactory;
  * ordered.
  */
 public class Certificate extends AcmeResource {
+    @Serial
     private static final long serialVersionUID = 7381527770159084201L;
     private static final Logger LOG = LoggerFactory.getLogger(Certificate.class);
 
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/Identifier.java b/acme4j-client/src/main/java/org/shredzone/acme4j/Identifier.java
index fc62bd61..40129050 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/Identifier.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/Identifier.java
@@ -17,6 +17,7 @@ import static java.util.Collections.unmodifiableMap;
 import static java.util.Objects.requireNonNull;
 import static org.shredzone.acme4j.toolbox.AcmeUtils.toAce;
 
+import java.io.Serial;
 import java.io.Serializable;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
@@ -37,6 +38,7 @@ import org.shredzone.acme4j.toolbox.JSON;
  * @since 2.3
  */
 public class Identifier implements Serializable {
+    @Serial
     private static final long serialVersionUID = -7777851842076362412L;
 
     /**
diff --git a/acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeRetryAfterException.java b/acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeRetryAfterException.java
index 97ffd18c..f8d45c06 100644
--- a/acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeRetryAfterException.java
+++ b/acme4j-client/src/main/java/org/shredzone/acme4j/exception/AcmeRetryAfterException.java
@@ -13,6 +13,7 @@
  */
 package org.shredzone.acme4j.exception;
 
+import java.io.Serial;
 import java.time.Instant;
 import java.util.Objects;
 
@@ -30,6 +31,7 @@ import org.shredzone.acme4j.AcmeJsonResource;
  */
 @Deprecated
 public class AcmeRetryAfterException extends AcmeException {
+    @Serial
     private static final long serialVersionUID = 4461979121063649905L;
 
     private final Instant retryAfter;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeJsonResourceTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeJsonResourceTest.java
index fd534d96..222ba0dc 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeJsonResourceTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeJsonResourceTest.java
@@ -17,6 +17,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.shredzone.acme4j.toolbox.TestUtils.getJSON;
 import static org.shredzone.acme4j.toolbox.TestUtils.url;
 
+import java.io.Serial;
 import java.net.URL;
 import java.time.Instant;
 import java.util.Optional;
@@ -140,6 +141,7 @@ public class AcmeJsonResourceTest {
      * Minimum implementation of {@link AcmeJsonResource}.
      */
     private static class DummyJsonResource extends AcmeJsonResource {
+        @Serial
         private static final long serialVersionUID = -6459238185161771948L;
 
         private int updateCount = 0;
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeResourceTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeResourceTest.java
index bec26da4..20082a0a 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeResourceTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/AcmeResourceTest.java
@@ -20,6 +20,7 @@ import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
+import java.io.Serial;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
 
@@ -113,6 +114,7 @@ public class AcmeResourceTest {
      * Minimum implementation of {@link AcmeResource}.
      */
     private static class DummyResource extends AcmeResource {
+        @Serial
         private static final long serialVersionUID = 7188822681353082472L;
         public DummyResource(Login login, URL location) {
             super(login, location);
diff --git a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeLazyLoadingExceptionTest.java b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeLazyLoadingExceptionTest.java
index e0f518f0..5f4dfa18 100644
--- a/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeLazyLoadingExceptionTest.java
+++ b/acme4j-client/src/test/java/org/shredzone/acme4j/exception/AcmeLazyLoadingExceptionTest.java
@@ -16,6 +16,7 @@ package org.shredzone.acme4j.exception;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.mock;
 
+import java.io.Serial;
 import java.net.URL;
 
 import org.junit.jupiter.api.Test;
@@ -47,6 +48,7 @@ public class AcmeLazyLoadingExceptionTest {
     }
 
     private static class TestResource extends AcmeResource {
+        @Serial
         private static final long serialVersionUID = 1023419539450677538L;
 
         public TestResource(Login login, URL location) {